1. Field of the Invention
The present invention relates to an asymmetrical signal detector, used for magnetic recording and communications, for detecting an asymmetrical quantity of an asymmetrical signal and to a signal regenerating apparatus using this detector.
2. Description of the Related Art
In the fields of magnetic recording and communications, there is a case where an input signal is asymmetrical with respect to positive and negative sides. For example, in the field of a magnetic recording apparatus, a read signal waveform tends to be asymmetrical with respect to the positive/negative sides because of adopting an MR (Magneto-Resistive) head. It is therefore necessary to detect an amplitude value of each of the positive/negative components as well as an amplitude error value between signal positive/negative components and an offset quantity and also compensate an asymmetrical signal.
FIGS. 24A and 24B are diagrams of assistance in explaining an operation of the MR head. FIG. 25 is a block diagram showing the prior art. FIG. 26 is an explanatory diagram showing an offset.
FIG. 24A illustrates an operation curve of the MR (Magneto-Resistive?) head used for a magnetic disc device. Record data are read by making use of the fact that a resistive rate .rho. of an MR element changes with respect to an input magnetic field H from a magnetic record medium. Generally, the head is biased to a bias magnetic field Hb. Accordingly, an output signal OUT becomes bipolar (+1, 0, -1).
Further, ideally, a linear area (straight line area) of this operation curve is used. Therefore, if an input signal IN (magnetic field recorded) is symmetrical with respect to the positive and negative sides, the output signal OUT also has a symmetrical signal amplitude with respect to the positive and negative sides.
FIG. 24B shows a case where a non-linear area on the operation curve is used because of the bias point Hb deviating. At this time, the output signal OUT becomes a signal that is asymmetrical with respect to the positive and negative sides.
FIG. 25 illustrates a construction of a signal processing system in a conventional magnetic recording/reproducing apparatus. As shown in FIG. 25, a magnetic recording/reproducing system 1 is constructed of a magnetic record medium and a magnetic head. A signal read by the magnetic head is inputted to an equalizer 3 via an AC coupling unit 2 composed of an amplifier and a filter. The equalizer 3 shapes a waveform of the signal inputted. Thereafter, a data detector 4 detects pieces of data [0], [1] from waveform-equalized signals. Thus, the magnetic recording/reproducing system 1 is linked via the AC coupling unit to the equalizer 3.
Referring to FIG. 26, the symbols IN1, IN2 designates signal waveforms before AC coupling. The symbol IN1 indicates the waveform that is symmetrical with respect to the positive and negative sides, while IN2 indicates an asymmetrical waveform with respect to the positive and negative sides. Further, the symbols OUT1, OUT2 represent signal waveforms after the AC coupling. The symbol OUT1 indicates a symmetrical waveform with respect to the positive and negative sides, while OUT2 indicates an asymmetrical waveform with respect to the positive and negative sides.
As illustrated in FIG. 26, if the signal is symmetrical with respect to the positive and negative sides, a 0-level of the signal never fluctuates. Whereas if the signal is asymmetrical with respect to the positive and negative sides, the 0-level fluctuates by V0. That is, an offset is produced.
In general, a linear type equalizer is employed. For this reason, when the input signal has a between-positive-negative asymmetrical signal amplitude, and when the offset is caused, there arises a problem in which the equalizer encounters difficultly in equalizing the signal to a desired waveform.
Further, a problem is that a deviation (equalizing error) from the desired waveform increases the liklihood of a subsequent misjudgment of [0], [1] on the part of the detector.
Besides, there exists a problem, wherein even detecting the amplitude value of such an asymmetrical signal becomes difficult due to the secondarily-produced offset.